Rocket projectile



M. L- RICE ETAL ROCKET PROJECTILE Sept. 24, 1963 Filed Sept. 18, 1957 2Sheets-Sheet l m l n l l ll l l I III IIIIIIQ 1 IPIVENTOR [Ila/imdleeKm? AGENT Sept. 24, 1963 M. L- RICE ETAL ROCKET PROJECTILE 2Sheets-Sheet 2 Filed Sept. 18, 1957 I III -Qw VXN I NV EN TOR 5flll/llmrdjeejla'ce llrv United States Patent This invention relates torocket-assisted projectiles. The object of this invention is to providerocket projectiles employing a liquid monopropellant, which, whenlaunched at Mach number velocities above 2, automatical- 1y compensatefor changes in aerodynamic drag to which the projectile is subjectedduring flight, thereby making possible maintenance of desired constantvelocity by the projectile rocket motor.

In the drawings:

FIG. 1 is a vertical, longitudinal, sectional view through a rocketprojectile showing an embodiment of the invention.

FIG. 2 is a vertical, transverse, cross-sectional view taken along line22 of FIG. 1.

FIG. 3 is a vertical, transverse cross-sectional view taken along line3-3 of FIG. 1.

FIG. '4 is a vertical, longitudinal, sectional view, with certain partsshown in elevation, showing the effect of increased ram pressure on theram pressure piston. with concomitant increased injection valve openingand also showing the position of the regenerative pumping piston afterdepletion of some of the liquid .monopropellant in the reservoir.

FIG. 5 is a vertical, longitudinal sectional view through a modificationof the device.

FIG. 6 is a fragmentary cross-sectional view taken along line 6-6 ofFIG. 5.

The maintenance of constant projectile velocity is frequently of greatimportance, as, for example, in the case of air to air missiles wherevariation in velocity introduces inaccuracies in the missile trajectorywhich may cause the missile to miss its target. Such projectiles aregenerally fired from rapidly moving aircraft so that the requisitelaunching velocity is imparted to the projectile both by the velocity ofthe plane and the propulsive effect of an ex ternal thrust-producingdevice, such as a gun. If the projectile is launched from a stationarypropulsive mechanism, as, for example, if fired from the ground, theexternal thrust produced by the firing device must be suf ficient tolaunch the projectile at the necessary high velocity.

Variation in aerodynamic drag on a projectile launched from a stationarydevice is primarily produced by changing altitude. In the case ofprojectiles launched from moving aircraft, variation in drag is alsocaused by variations in aircraft velocity relative to the atmosphere,where the launching velocity or the projectile relative to the launchingcraft is fixed. To maintain the moving projectile at a constantvelocity, the thrust or velocity-producing force engendered by therocket motor must vary with changes in aerodynamic drag. In other words,it must increase with increasing drag and decrease with decreasing drag.

This invention comprises a liquid-monopropellant rocket projectile whichautomatically compensates for variation in aerodynamic drag by varyingthe thrust produced by the rocket motor with the air pressure on thenose of the high velocity projectile. Air pressure at the nose of themoving projectile, namely ram pressure, is approximately proportional tothe ambient pressure, namely atmospheric pressure at the given altitude,times the square of the projectile Mach number. At the usual velocitiesice of air-launched rocket projectiles, namely at velocities above aMach number of 2, the ram pressure is proportionalto the aerodynamicdrag, so that the device of this invention, by providing means formaking the thrust responsive to ram pressure, thereby automaticallyovercomes the effect of changes in aerodynamic drag on projectilevelocity.

The liquid monopropellantemployed in the projectile rocket motor cancomprise a single compound, such as hydrogen peroxide, nitromethane ortetranitromethane, which contains molecularly-combined oxygen insufiicient amount for internal combustion of other componentsof thecompound, or a mixture comprising a fuel and an oxidizing agent, such asa mixture of hydrazine, nitric acid and water or a slurry of keroseneand ammonium perchlorate.

Broadly speaking, the propulsive mechanism of the projec-tile comprisesa rearwardly positioned rocket motor comprising a combustion chamberventing rearwardly through a nozzle or nozzles of fixed diameter, aliquid monopropellant reservoir forward of the combustion chambercommunicating with the combustion chamber through a valve port ofvariable cross-sectional throat area opening into the forward end of thecombustion chamber for injection of the liquid propellant, means forforcing flow of the propellant into the combustion chamber and afloating differential piston axially positioned in the projectileforward of the combustion chamber, the forward larger face of which isresponsive to ram pressure at the nose of the projectile and the reducedrearward end of which is responsive to combustion chamber pressure andfunctions as a slidable valve member seated in and controlling theeffective cross-sectional throat area of the propellant injection valveport and, thereby, the mass flow rate of the propellant.

The floating differential piston acts as a balancing means between rampressure and the pressure in the combustion chamber. When ram pressureon the forward face of the piston increases, the piston moves rearwardlyand, by proper design of the rear valve end, increases the size of theinjection port opening into the combustion chamber to a controlleddegree, thus increasing the amount of propellant injected into thecombustion chamber in an amount proportional to the increase in rampressure. The pressure in the combustion chamber rises, therebyincreasmg the forward thrust produced by the highvelocity gas streamissuing from the rear nozzle of the rocket motor.

Since, as aforementioned, ram pressure is proportional to aerodynamicdrag, the increased thrust produced by the motor overcomes the increasein drag and maintains the projectile at constant velocity. V

Conversely, when ram pressure decreases, as with in creasing altitude,the pressure in the combustion chamber overbalances the force exerted byram pressure, the differential piston moves forward, the cross-sectionalthroat area of the propellant-injection valve port is decreased in size,reducing the amount of propellant introduced into the combustionchamber, combustion chamber pressure drops, thrust on the projectiledecreases in an amount compensating for the reduction in aerodynamicdrag and the projectile is maintained at constant velocity.

In a liquid monopropellant rocket the mass flow rate of the propellantinto the combustion chamber determines the combustion chamber pressureand consequently the rocket thrust. Under equilibrium conditions themass flow rate of the propellant into the chamber is proportional to thechamber pressure and the rocket thrust.

The propellant injection valve, therefore, must be so designed thatchange in the mass flow rate of propellant is proportional to the changein ram pressure. The mass d flow rate Q of the propellant into thecombustion chamber is substantially given by the following equation:

where p is propellant density, AP is the pumping pressure, namely thedifference in pressure between that on the liquid forcing it out of thereservoir and combustion chamber pressure, and A is the valve orificearea. By calculating these factors on the basis of particularconditions, the injection valve can then readily be designed so that fora given motion of the piston produced by variation in ram pressure, thesize of the injection valve port throat area will be change to therequisite extent to provide for the proportional change in propellantflow rate necessary to adjust combustion chamber pressure and, thereby,thrust, to the change in aerodynamic drag.

FIGURES 1 through 4 illustrate a device embodying the principles of theinvention.

The projectile 1 contains a war head 2 at its forward end and a rocketmotor comprising a combustion chamber 3 and rearwardly venting nozzles 4of predetermined,

fixed size. The liquid monopropellant is stored in reservoir 5 and feedsinto the combustion chamber through orifice 6 in the propellantreservoir, communicating channel 7, aperture 8 and annular channel 9from which it is injected into the forward end of the combustion chamberthrough the rearwardly flaring valve port 10 of variable cross-sectionalthroat area.

In the device shown, the pumping pressure for injection of the liquidpropellant into the combustion chamber is provided by a regenerativesystem in which the combustion chamber pressure acting on the rearlarger face 11 of floating differential piston 12, which will hereafterbe characterized as the pumping piston, is employed as the injectingforce. The differential pumping piston comprises a rearward annular disc13 which functions as the insulated separating wall between thereservoir and the combustion chamber. Cylindrical hollow piston stem 14,of considerably reduced diameter, extends forward longitudinally frompiston disc 13 the entire length of the propellant reservoir, formingthe interior wall of the annular reservoir chamber and terminating atits forward end 15 at a point beyond the forward end of the reservoirchamber when the chamber is at maximum size. The forward face 34 ofpiston disc 13, which is acted on by the pressure of the liquid in thereservoir, has a smaller surface area than rear face 11 because ofpiston stem 14. Bore 16 in the hollow piston stem is continuous withhere 17 in the large disc end of the pumping piston, which opens intothe combustion chamber. Orifice 6 providing for fluid flow from thereservoir is located in the rear end of the pumping piston stem andopens into channel 7, which is a longitudinal groove in the interiorwall of the hollow stem terminating at a point rearward of the forwardend of the stem. Fixed cylindrical tube 18, having an outer diametersubstantially equal to the diameter of the pumping piston stem bore,extends longitudinally from the rear face of the differential pumpingpiston at its rearwardmost position through the pumping piston stern andextends forward of the anterior end 15 of the pumping piston for adistance at least equal to the greatest length of the reservoir, namelythe length of the reservoir when filled with the maximum amount of theliquid propellant. The forward end of the hollow pumping piston stemextends into and is free to move forward in annular channel 19 definedinteriorly by the outer wall of tube 18 and exteriorly by the interiorwall 20 of the cylindrical annular war head. Annular channel 19 extendsforward from face 15 of the pumping piston stem for a distance at leastequal to the greatest length of the propellant reservoir when thepumping piston is at its rearwardmost position. The channel is open tothe atmosphere through side vent 21 so that the pressure within it isambient.

Axially positioned anteriorly of the combustion cham- 4 V her, is asecond floating differential piston 22, which will be characterizedhereafter as the ram pressure piston, oriented in such manner that thelarger end 23 of the piston, which is a disc slidably seated in pistonchamber 24 in the forward end of the projectile, faces forwardly, and

the smaller valve end 25 of the piston, having the smaller face 26,faces rearwardly. The large disc end and smaller valve end of thedifferential ram pressure piston are joined by cylindrical piston stem27 which extends axially and longitudinally through axial bore 28 infixed tube 18. The piston stem, which fits closely in the anteriorportion of bore 28, is narrowed to a smaller diameter at a pointslightly forward of aperture 8 in tube 18 to form annular channel 9 forflow of the liquid propellant. The inner wall at the rear end of tube 18flares rearwardly to form valve port 10 of variable cross-sectionalthroat 7 area for injection of the propellent'liquid into the combustionchamber. The rear end of the ram pressure piston forms a rearwardlyflaring valve member 25 which is slidably. positioned in similarlyflaring valve port 10, so that face 26 of the ram pressure piston isexposed to the pressure of the gases in the combustion chamber. As theram pressure piston moves forward or backward, the

cross-sectional venting throat area of injection valve port 11 becomesrespectively larger or smaller with corresponding increase or decreasein the mass flow rate of the propellant into the combustion chamber.

Channel 29, which extends forward longitudinally and axially from pistonchamber 24 and opens to the atmos- I phere in the nose 30 of theprojectile, provides an open passage for entry of air at the highcompressional pressure incident at the nose into the piston chamber sothat the ram pressure on the nose of the projectile is duplicated on theforward face 31 of the piston. Spring 32 of predetermined design andtensional characteristics is positioned back of piston disc 23. Shoulder33 in the piston chamber prevents forward motion of the piston to the (Ptimes the surface area of face 11 (A minus lamb? ent atmosphericpressure (P times the area of the forward face 15 (A of the pumpingpiston, the latter force being substantially negligible. The pressure inthe reservoir (P is given by the following equation:

where A is the area of piston face 34. Since A is smaller than A and P Ais quite small, the pressure in the reservoir is higher than that in thecombustion chamher and provides a positive pumping pressure P, which isequal to P -P As the liquid propellant is depleted in the reservoir, thefloating differential pumping piston is moved forward by combustionchamber pressure and the pumping pressure in the reservoir ismaintained. The position of the pumping piston after depletion of someof the propellant in the reservoir is shown in FIG- URE 4.

The com-bustion gases produced by burning of the liquid monopropell-antin the combustion chamber vent rearwardly through the restricted nozzles4 as high velocity gas streams which produce a forward thrust on theprojectile. The combustion gases also exert pressure on rear face 26 ofthe ram pressure piston, the total force on the piston equaling thecombustion chamber pressure times the area of the piston valve face. Theram pressure at the nose of the rapidly moving projectile iscommumidated through passage 29 and exerts an opposing force on forwardface 31 of the ram pressure piston equal to the ram pressure times thearea of face 31. Since combustion chamber pressures in a liquidpropellant system are relatively .low, rarely exceeding about 200 to 300p.s.i., and the valve end of the ram pressure piston is relatively smallthe high ram pressures normally incident on the high velocity projectileare likely to push the piston rearwardly to such an extent as to keepthe valve Wide open at all times. Spring 32 functions to reduce theeffect of ram pressure in an amount which, being proportional tovariations in ram pressure, does not counteract the over-allcounterbalancing of ram and combustion chamber pressures.

When the opposing forces on the ends of the springretarded floatingdifferential ram pressure piston balance, the piston remains stationary.When ram pressure increases the piston moves rearwardly, as shown inFIG- URE 4, to increase venting throat area of injection valve 19 to theextent required to increase the mass flow rate of the propellant,thereby increasing combustion chamber pressure, which produces thedesired increase in thrust to overcome the higher aerodynamic drag.

Reduction in ram pressure reduces the force exerted on forward face 31of the piston. The opposing combustion chamber pressure pushes thepiston forward, thereby reducing venting throat area of injection valve19, reducing combustion chamber pressure and reducing thrust in aproportional amount.

The number of fluid feeding orifices in the reservoir can be varied asdesired. The design of the ram pressure piston valve and injection portcan also be modified so long as they are properly designed toproportionate the desired increase and decrease in mass flow rate withchange in ram pressure as aforediscussed.

Although the specific embodiment shows a regenerative fluid injectionsystem employing a differential piston to provide pumping pressure,conventional pumping means can also be used, as shown in FIGURES 5 and6.

The modification shown in FIG. 5 is substantially similar to the deviceshown in FIG. 1 in many respects, including the floating differentialram pressure piston and its mode of functioning in the device, the chiefdifference being that a conventional pump 35 replaces the 1 egenerativepumping piston system. Similar elements are designated by correspondingreference numerals.

The projectile 1 contains a war head 2 at its forward end and 'a rocketmotor comprising a combustion chamher 3 and rearw-ardly venting nozzle4a of predetermined, fixed size. voir 5a and is fed into the combustionchamber by means of pump 35, shown diagrammatically, through orifice 36into annular channel 9a from which it exit through the rearwardly flarinvalve port 10a of variable crosssectional throat area.

Floating differential piston 22. is axially positioned anteriorly of thecombustion chamber, with its for-Ward, larger spring retarded disc end23 slidably seated in piston chamber 24, its stem 27 extendingrearwardly land axially through longitudinal axial bore 37 within fixedtube 33, formed in part by the interior wall 39 of the annular casingcontaining the war head and in part by the interior Wall 49 of theannular reservoir chamber, and its rear, flaring valve end 25 extendinginto ilmng port we open ing into the forward end of the combustionchamber. The rear, smaller face 26 of the differential piston is therebyexposed to and responsive to the pressure of the gases in the combustionchamber. The piston stem fits closely in here 37 until a point justforward of propellantfeeding orifice 36 in the reservoir, where itnarrows in diameter to form an annular channel 9a for passage of theliquid propellant into the injection valve. As the differential pistonmoves forward or backward under the opposing ram and'com'bustion chamberpres-sures, the

cross-sectional venting throat area of injection valve port 10:: becomesrespectively larger or smaller with corre- The liquid :monopropellant isstored in resersponding increase or decrease in the mass flow rate ofthe propellant into the combustion chamber.

Forward piston chamber 24 is open to the atmosphere through channel 29which opens into the nose of the projectile, so that the forward largerface 31 of the differential piston is acted on and is responsive to rampressure on the nose of the rapidly movingprojectile. Spring 32functions similarly to that in the device of FIG. 1 and shoulder 33similarly prevents total closure of the injection valve port.

The diiferential piston functions in the same way as the ram pressurepiston of the device of FIG. 1 in compensating for variation inaerodynamic drag and thereby maintaining the projectile at constantvelocity. Increase in ram pressure, which, as aforedescribed, issubstantially proportional to increase in aerodynamic drag at the highprojectile velocities, forces the piston rearwardly with resultinincrease in valve aperture and increase in mass flow rate of thepropellant, thereby increasing combustion chamber pressure, whichproduces the increased thrust necessary to compensate for the increaseddrag. When aerodynamic drag and ram pressure drop, the piston movesforward, reducing the rate of propellant injection and Combustionchamber pressure, thereby reducing thrust to a compensating degree.

The specific design of a given projectile in tenms, for example, of theparticular surface area ratio of the differential ram pressure piston,the degree of variation in the propellant injection valve throat area,the particular monopropel-lant used, the size and number of the rear jetnozzles and the like, is, of course, determined by the particularrequirements, such as the weight, size and shape of the projectile, thedesired velocity and the particular launching conditions. These arefactors which can readily be calculated by anyone versed in the art.

lthough this invention has been described with reference to illustrativeembodiments thereof, it will be apparent to those skilled in the artthat the principles of this invention may be embodied in other forms butwithin the scope of the claims.

We claim:

1. In a rocket-assisted projectile, a posteriorly positioned combustionchamber adapted to burn a liquid monopropellant and having at least onerear nozzle for producing forward thrust by rearward discharge of highvelocity combustion gases, an annular reservoir chamber forward of saidcombustion chamber adapted to contain liquid monopropellant, pumpingmeans for forcing said monopropell-ant out of the reservoir and into thecornbustion chamber, a floating differential piston axially positionedanteriorly of said combustion chamber, the forward larger face of saiddiiferential piston being in open communication with and directlyresponsive to ram pressure on the nose of the projectile, and thesmaller rear portion of said differential piston forming a valve memberaxially and slidably positioned in a port of variable cross-sectionalthroat area opening posterior-1y into the forward end of the combustionchamber, whereby the smaller rear face of the differential piston isacted on and is directly responsive to combustion chamber pressure, saidport being in communication with the liquid venting orifice of themonopropellant reservoir and forming an exit passage into the combustionchamber for the liquid monoprope llant flowing therefrom, the rearpiston valve member having a configuration relative to that of the portsuch that rearward motion of the piston valve member increases thecross-sectional throat area of said port for increased passage ofmonopropellant into the combustion chamber and forward motion decreasesthe cross-sectional throat area, the mass flow rate of themonopropellant being injected into the combustion chamber, thereby beingcontrolled by the forward or rearward motion of the differential pistonin response to variation in ram pressure on the nose of the projectilerelative to combustion chamber pressure.

2. The projectile of claim 1 in which the forward, larger end of thefloating differential piston is slidably seated in a chamber which is inopen communication with the nose of the projectile and in which saidpiston is associated with means for reducing to a predetermined andproportionate degree its rearward motion in response to ram pressure.

3.- In a rocket-assisted projectile, a posteriorly positioned combustionchamber adapted to burn a liquid monopropellant and having at least onerear nozzle for producing forward thrust by rearward discharge of highvelocity combustion gases; an annular reservoir cham ber forward of saidcombustion chamber and adapted to contain liquid monopropellant, pumpingmeans for forcing said liquid monopropellant out of the reservoir andinto the combustion chamber, and a floating differential piston axiallypositioned anteriorly of said combustion chamber, said piston comprisinga forward larger disc end slidably positioned in a chamber which is inopen communication with the nose of the projectile, whereby the forward,larger face of the piston is acted on and is directly responsive to nampressure on the nose of the projectile, said forward end of the pistonbeing associated with means for reducing to a predetermined andproportionate degree rearward motion of said piston in response to rampressure, a piston stem of reduced diameter extending axially andlongitudinally through an axial bore within a fixed longitudinal tubeopening rearward-1y into the forward end of the combustion chamber,said'bore being in communication with the liquid-venting orifice in thereservoir, the rear portion of said bore flaring rearwardly posteriorlyof the entrance of propellant liquid into the bore, thereby forming anexit passage port of variable cross-sectional throat area into thecombustion chamber for the liquid monopropellant, and a rear portion ofreduced diameter relative to the forward piston disc, said rear portionflaring rearwardly and being slidably seated in said port, whereby therear face of the differential piston is acted on and is directlyresponsive to combustion chamber pressure, variation in thecross-sectional throat area of said port and, thereby, the mass flowrate of the monopropellant liquid being injected into the combustionchamber, being controlled by the forward or rearward motion of thedifferential piston in response to variation in ram pressure on the noseof the projectile relative to combustion chamber pressure,

4. The projectile of claim 3 in which the means for reducing rearwardmotion of the differential piston in response to ram pressure is aspring urging the differential piston in a direction opposite to the rampressure force.

5. The projectile of claim 1 in which the pumping means for forcing theliquid monopropellant out of the reservoir is a second floatingdifferential piston comprising a centrally perforated, annular discforming a slidable wall between the combustion chamber and themonopropellant reservoir forward thereof, the rear face of the discbeing responsive to combustion chamber pressure and the forward facebeing responsive to the pressure of the liquid monopropellant in thereservoir, and a hollow tube, of substantially reduced exterior diameterrelative to the diameter of said disc, attached to and reducing the areaof the forward face of said disc and extending forward longitudinally tothe axis of the projectile, the bore of the tube and the perforation inthe disc being in registry,

said hollow tube member of the pumping differential piston forming theinterior wall of the annular monopropellant reservoir chamber andterminating forward of the reservoir chamber within an annular channelin which it is slidably positioned, which extends forward of said hollowtube pumping-piston member for the desired distance of forward travel ofthe pumping piston and which is in communication with the atmospherethrough a side venting channel whereby pressure on the forward annularface of the reduced end of the pumping differential piston is ambient.

6. The projectile of claim 2 in which the pumping means for forcing theliquid monopropellant out of the reservoir is a second floatingdifferential piston comprising a centrally perforated, annular discforming a slidable wall between the combustion chamber and themonopropellant reservoir forward thereof, the rear face of the discbeing responsive to combustion chamber pressure and the forward facebeing responsive to the pressure of the liquid monopropellant in thereservoir, and a hollow tube, of substantially reduced exterior diameterrelative to the diameter of said disc, attached to and reducing the areaof the forward face of said disc and extending forward longitudinally tothe axis of the projectile, the bore of the tube and the perforation inthe disc being in registry, said hollow tube member of the pumpingdifferential piston forming the interior wall of the annularmonopropellant reservoir chamber and terminating forward of thereservoir chamber within an annular channel in which it is slidablypositioned, said annular channel extending forward of said hollow tubepumping-piston member for the desired distance of forward travel of thepumping piston and being in communication with the atmosphere through aside venting channel whereby pressure on the forward annular face of thereduced end of the pumping differential piston is ambient.

7. The projectile of claim 3 in which the pumping means for forcing theliquid monopropellant out of the reservoir is a second floatingdifferential piston comprising a centrally perforated, annular discforming a slidable wall between the combustion chamber and themonopropellant reservoir forward thereof, the rear face of the discbeing responsive to combustion chamber pressure and the forward facebeing responsive to the pressure of the liquid monopropellant in thereservoir, and a hollow tube, of substantially reduced exterior diameterrelative to the diameter of said disc, attached to and reducing the areaof the forward face of said disc and extending forward longitudinally tothe axis of the projectile, the bore of the tube and the perforation inthe disc being in registry, said hollow tube member of the pumpingdifferential piston forming the interior wall of the annularmonopropellant reservoir chamber and terminating forward of thereservoir chamber within an annular channel in which it is slidablypositioned, which extends forward of said hollow tube pumping-pistonmember for the desired distance of forward travel of the pumping pistonand which is in communication with the atmosphere through a side ventingchannel whereby pressure on the forward annular face of the reduced endof the pumping differential piston is ambient.

8. The projectile of claim 4 in which the pumping means for forcing theliquid monopropellant out of the reservoir is a second floatingdifferential piston comprising a centrally perforated, annular discforming a slidable wall between the combustion chamber and themonopropellant reservoir forward thereof, the rear face of the discbeing responsive to combustion chamber pressure and the forward facebeing responsive to the pressure of the liquid monopropellant in thereservoir, and a hollow tube, of substantially reduced exterior diameterrelative to the diameter of said disc, attached to and reducing the areaof the forward face of said disc and extending forward longitudinally tothe axis of the projectile, the bore of the tube and the perforation inthe disc being in registry, said hollow tube member of the pumpingdifferential piston forming the interior wall of the annularmonopropellant reservoir chamber and terminating forward of thereservoir chamber within an annular channel in which it is slidablypositioned, which extends forward of said hollow tube pumping-pistonmember for the desired distance of forward travel of the pumping pistonand which is in communication with the atmosphere through a side ventingchannel whereby pressure on the forward annular face of the reduced endof the pumping differential piston is ambient.

9. The projectile of claim 7 in which the slidable hollow tube member ofthe pumping differential piston forming the interior wall of the annularreservoir chamber has at least one rearwardly positioned orifice forventing of the monopropellant liquid feeding into a channel extendingforward longitudinally from said orifice and defined by a longitudinalgroove in the interior wall of said hollow tube member, said grooveterminating rearwardly of the forward end of said hollow tube, and theexterior wall of the fixed longitudinal tube housing the axial bore inwhich the axial piston stem of the diflerential piston responsive to rampressure is slidably seated, said channel communicating with an orificein said fixed longitudinal tube positioned in a transverse planesubstantially adjacent the forward end of the monopropellant reservoir,the orifice in said fixed longitudinal tube in turn feeding themonopropellant liquid into an annular channel within the axial boredefined by the interior wall of the fixed longitudinal tube and theaxial piston stem, the axial piston stem being of reduced diameterrelative to the diameter of the axial bore rearwardly from a pointforward of the orifice in the fixed longitudinal tube until the pistonstem flares rearwardly to form the valve member seated in themonopropellant injection port which forms the exit passage of themonopropellant liquid from said annular channel within the axial boreinto the combustion chamber.

10. The projectile of claim 8 in which the slidable hollow tube memberof the pumping differential piston forming the interior wall of theannular reservoir chamber has at least one rearwardly positioned orificefor venting of the monopropellant liquid feeding into a channelextending forward longitudinally from said orifice and defined by alongitudinal groove in the interior wall of said hollow tube member,said groove terminating rearwardly of the forward end of said hollowtube, and the exterior wall of the fixed longitudinal tube housing theaxial bore in which the axial piston stem of the differential pistonresponsive to ram pressure is slidably seated, said channelcommunicating with an orifice in said fixed longitudinal tube positionedin a transverse plane substantially adjacent the forward end of themonopropellant reservoir, the orifice in said fixed longitudinal tube inturn feeding the monopropellant liquid into an annular channel withinthe axial bore defined by the interior wall of the fixed longitudinaltube and the axial piston stem, the axial piston stem being of reduceddiameter relative to the diameter of the axial bore rearwardly from apoint forward of the orifice in the fixed longitudinal tube until thepiston stem flares rearwardly to form the valve member seated in themonopropellant injection port which forms the exit passage of themonopropellant liquid from said annular channel within the axial boreinto the combustion chamber.

References Cited in the file of this patent UNITED STATES PATENTS2,550,678 Deacon May 1, 1951 2,700,337 Cumming Ian. 25, 1955 2,780,914Ring Feb. 12, 1957 2,868,127 Fox Jan. 13, 1959

1. IN A ROCKET-ASSISTED PROJECTILE, A POSTERIORLY POSITIONED COMBUSTIONCHAMBER ADAPTED TO BURN A LIQUID MONOPROPELLANT AND HAVING AT LEAST ONEREAR NOZZLE FOR PRODUCING FORWARD THRUST BY REARWARD DISCHARGE OF HIGHVELOCITY COMBUSTION GASES, AN ANNULAR RESERVOIR CHAMBER FORWARD OF SAIDCOMBUSTION CHAMBER ADAPTED TO CONTAIN LIQUID MONOPROPELLANT, PUMPINGMEANS FOR FORCING SAID MONOPROPELLANT OUT OF THE RESERVOIR AND INTO THECOMBUSTION CHAMBER, A FLOATING DIFFERENTIAL PISTON AXIALLY POSITIONEDANTERIORLY OF SAID COMBUSTION CHAMBER, THE FORWARD LARGER FACE OF SAIDDIFFERENTIAL PISTON BEING IN OPEN COMMUNICATION WITH AND DIRECTLYRESPONSIVE TO RAM PRESSURE ON THE NOSE OF THE PROJECTILE, AND THESMALLER REAR PORTION OF SAID DIFFERENTIAL PISTON FORMING A VALVE MEMBERAXIALLY AND SLIDABLY POSITIONED IN A PORT OF VARIABLE CROSS-SECTIONALTHROAT AREA OPENING POSTERIORLY INTO THE FORWARD END OF THE COMBUSTIONCHAMBER, WHEREBY THE SMALLER REAR FACE OF THE DIFFERENTIAL PISTON ISACTED ON AND IS DIRECTLY RESPONSIVE TO COMBUSTION CHAMBER PRES-